Ms Thompson's story pays testament to a law which was passed in the U.S. in 1967. The Age Discrimination in Employment Act was made to protect workers aged 40 and over from ageism in the workplace.

But other women are not quite so confident.

Stephanie Martinez Kluga, a manager at Insperity which is a San Antonio-based human resources company, said ageism is still alive and well.

'Some men and women may still encounter ageism in the workplace,’ she said. ‘The long-standing perception that men with grey hair are experienced and women with grey hair are simply old may still be an issue that affects employees across the U.S.'

Grey panthers are aiming to ensure these perceptions are soon eliminated.

Anne Kreamer, the author of several books including 2007's Going Grey, said women need a reality check when it comes to dying their hair over greys.

'We only fool ourselves about how young we look with our dyed hair,' the former Nickelodeon executive, who dyed her own hair for 25 years, said.

She added that 95per cent of women in today's workforce dye their hair in the hope of appearing younger.

Essie Weingarten, a 62-year-old founder and creative director of the nail polish company Essie Cosmetics, gave up colouring her hair about 20 years ago. She began going grey at the age of 18 and had coloured her hair for years.

She said: 'People would say, "Are you going crazy? You have to colour your hair". I had my own business. I was an entrepreneur. I could do whatever I wanted but the truth is I know a lot of women who are petrified to show grey hair because it means they’re maturing.'